Immersion platinum plating solution

ABSTRACT

A platinum plating solution for immersion plating a continuous film of platinum on a metal structure. The immersion platinum plating solution is free of a reducing agent. The plating process does not require electricity (e.g., electrical current) and does not require electrodes (e.g., anode and/or cathode). The solution includes a platinum source and a complexing agent including Oxalic Acid. The solution enables immersion plating of platinum onto a metal surface, a metal substrate, or a structure of which at least a portion is a metal. The resulting platinum plating comprises a continuous thin film layer of platinum having a thickness not exceeding 300 Å. The solution can be used for plating articles including but not limited to jewelry, medical devices, electronic structures, microelectronics structures, MEMS structures, nano-sized or smaller structures, structures used for chemical and/or catalytic reactions (e.g., catalytic converters), and irregularly shaped metal surfaces.

FIELD OF THE INVENTION

This invention relates to immersion plating of platinum onto a metalsurface, including for example immersion plating of a continuous thinfilm layer of platinum on a metal surface.

BACKGROUND OF THE INVENTION

Platinum is a precious metal for which there are many uses, bothindustrial and non-industrial. Many of these applications take the formof platinum plating, where platinum is plated on a metal surface orsubstrate. For example, the automotive industry uses platinum plating inthe production of catalytic converters. Platinum plating is also used tocoat medical instruments and devices, such as catheters or electricalcontacts on medical devices and surgical instruments. Platinum is alsoused in the electronics and electrical industries for electricalcontacts. Platinum coated electrodes are also used in the processes forrefining oil and manufacturing fertilizers and explosives. As a finalexample, platinum is used in the jewelry industry to plate lessexpensive metals. Platinum has a high luster and is resistant totarnishing and oxidation. Further, platinum resists oxidation and doesnot oxidize at high temperatures such as those encountered in hotexhaust gases from combustion engines and the like. Platinum is alsohypoallergenic.

However, platinum is very expensive. Therefore, any plating processpreferably will minimize the waste of platinum. For example, it ispreferable that a plating process deposit platinum only on the targetsurface and not on other surfaces. The deposition of platinum onto acontainer holding the plating solution, onto jigs or fixtures holdingthe object to be plated (e.g., a workpiece), or onto electrodes or otherequipment used in the plating process, is wasted platinum. It is alsopreferable that platinum be deposited to the minimum desired thickness.Overplating results in a platinum plating that is thicker than required,which means that more platinum was used in the plating process ascompared to a thinner but still adequate plating. Overplating and wastedplatinum not only require more platinum to be used than is necessary,but are also reflected in the cost of the article(s) being plated.Ideally, only the minimal amount of platinum needed would be used forplating articles, thereby reducing platinum costs and the platinumrelated costs of the article(s) being plated.

There are two conventional approaches to platinum plating:electroplating and electroless plating. In electroplating, twoelectrodes are immersed in a solution of electrolyte containing platinumions. The voltage difference between and anode and cathode creates anelectric field (e.g., an electrical current) in the solution, whichfacilitates the plating of a film of platinum onto the object. Theobject being plated may serve as one of the electrodes, for example.However, electroplating suffers from several drawbacks. One drawback isthat the process is directional. Therefore, it is more difficult toevenly plate irregularly shaped objects. Depending on the physicalsetup, the platinum may also coat the electrodes or fixtures, resultingin more waste.

In contrast, electroless plating does not use electrodes but uses areducing agent to facilitate a chemical reaction for plating a metalsubstrate. Typically, the metal substrate to be plated is submerged inan electroless plating solution that contains both platinum ions and areducing agent. The platinum ions are reduced to elemental platinum thatplates onto the metal substrate. Electroless plating also hasdisadvantages, some due to the use of the reducing agent. For example,the reducing agent is active regardless of whether a metal substrate issubmerged in the plating solution, because platinum is always present inthe solution. Thus, the chemical reaction in the electroless platingsolution continues even if no metal substrate is present. The solutionwill consume itself or “plate out”, requiring the replenishment of morechemicals and platinum and driving up the cost. Not only doeselectroless platinum plating drive up the cost, more importantly, the“plating out” of the bath means once the platinum is totally consumed,one cannot plate any more. The bath is basically dead. Bath stability isanother issue that affects the cost and efficiency of electrolessplating. As the bath decomposes, expensive platinum is wasted and thebath and associated tools covered by the bath are contaminated withplatinum residue. The platinum residue is difficult to remove.

There are continuing efforts to improve platinum plating technology.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings;

FIG. 1 depicts an example flow diagram of a method for an immersionplatinum plating solution;

FIG. 2 depicts a cross-sectional view of an example of an immersionplatinum plating apparatus and an article to be plated using animmersion platinum plating solution that is free of a reducing agent andthe plating process does not require electricity and electrodes; and

FIG. 3 depicts a cross-sectional view of another example of an immersionplatinum plating apparatus and an article to be plated using animmersion platinum plating solution that is free of a reducing agent andthe plating process does not require electricity and electrodes;

Although the above-described drawings depict various examples of theinvention, the invention is not limited by the depicted examples. It isto be understood that the drawings are not necessarily to scale.

DETAILED DESCRIPTION

Aspects of the invention provide a process for plating a metal surface(or substrate) with a continuous film of platinum using immersionplating. For purposes of this disclosure, the terms immersion platingand electroless plating are meant to be mutually exclusive. Electrolessplating uses a plating solution that contains a reducing agent.Immersion plating uses a plating solution that is free of a reducingagent. One advantage of immersion plating is that the plating solutiontypically is more stable and lasts longer because there is no reducingagent. In contrast, in electroless plating, the plating solution “platesout” and has to be replenished due to the presence of the reducingagent, even when no metal substrate is submerged in the platingsolution.

An aqueous immersion platinum plating solution is formed by combiningwater, a platinum source, a complexing agent and possibly various otheradditives. The platinum source provides the platinum for the plating. Insome applications, adding water may not be necessary if the platinumsource and/or complexing agent already include a sufficient volume ofwater. Platinum sources can be classified according to their oxidationstate, with Pt (II) sources and Pt (IV) sources being the more common.Examples of Pt (II) sources include but are not limited to thefollowing: Sodium Tetrachloroplatinate Na₂PtCl₄; DiammoniumTetrachloroplatinate (NH₄)₂[PtCl₄]; Potassium TetrachloroplatinateK₂PtCl₄; Ammonium Tetrachloroplatinate (NH₄)₂PtCl₄; and DiammineDinitritoplatinum Pt(NH₃)₂(NO₂)₂. Examples of Pt (IV) sources includebut are not limited to the following: Chloroplatinic Acid H₂PtCl₆;Sodium Hexachloroplatinate Na₂PtCl₆; Potassium HexachloroplatinateK₂PtCl₆, and Ammonium Hexachloroplatinate (NH₄)₂PtCl₆.

The complexing agent is used to control the reaction rate ofdisplacement of platinum. In one embodiment, Oxalic Acid (H₂C₂O₄) isused as the main complexing agent. Examples of other complexing agentsthat can be combined with Oxalic Acid include but are not limited to oneor more of the following compounds: Citric Acid; Acetic Acid (CH₃COOH);Sulfonic Acid; Thiourea (CSN₂H₄ or (NH₂)₂CS); Ethylenediamine (EDA);Monoethanolamine (MEA); Ethylediaminetetraacetic Acid (EDTA); Prydine(C₅H₅N); Hydroxylamine (NH₂OH); Acetylcysteine; Acetylacetone, andGlycine (NH₂CH₂COOH). These complexing agents when combined with OxalicAcid can be used to improve the quality of the deposited platinum film.

FIG. 1 depicts a flow diagram 100 of one example method for an immersionplatinum plating solution. At a stage 101, a platinum plating source(e.g., an aqueous solution of Pt (II) or Pt (IV)) is provided. At astage 103, a complexing agent (e.g., an aqueous solution of Oxalic Acid(H₂C₂O₄) is provided. At a stage 105, the platinum source and thecomplexing agent are mixed (e.g., they are added to each other) to forman immersion platinum plating solution. Any one or more of the stages101, 103, and 105 can optionally include adding water (e.g., a purifiedwater or deionized water) to form the immersion platinum platingsolution. At a stage 107, one or more additives can optionally be addedto the immersion platinum plating solution as will be described ingreater detail below. At a stage 109, the immersion platinum platingsolution, with or without the additives of stage 107, can optionally beapplied to a metal substrate to be plated with the immersion platinumplating solution. As will be described below, the applying 109 can beaccomplished in a variety of ways, including submerging an article to beplated in the solution and spraying the solution on the article to beplated. The applying can be performed under environmental conditionsthat are application dependent such as at a controlled temperature,pressure, plating time, solution pH, and/or a relative movement betweenthe solution and the article(s) being plated, for example. Optionally,after the stage 109, the article that was plated can be rinsed off (notshown) using an appropriate solution such as purified or deionizedwater, for example. Moreover, any time during or after the stage 109,the article(s) being plated can be inspected for plating quality asdescribed below. The immersion plating of an article at the stage 109occurs without the application of electricity (e.g., electrical currentand without the use of electrodes (e.g., anodes and/or cathodes).

One can use single or multiple complexing agents. The main purpose is tocontrol the stability and deposition rate of platinum film. Grain sizecontrol is another important factor. In one embodiment, the platinumsource is a Pt (II) source and the complexing agent is Oxalic Acid. ThePt (II) source has a molar concentration of not less than 0.5 mM, andpreferably has a molar concentration of between about 1 mM and about 50mM. Too low concentrations of the platinum source can result in a lowquality platinum film. Higher concentrations can become expensive due tothe greater quantity of platinum required. The molar concentration ofthe platinum source can be selected to balance factors such as the costof the bath (e.g., cost due to the amount of platinum in the platinumsource), the speed of platinum deposition, and the desired quality ofthe continuous platinum film. The Oxalic Acid preferably has a molarconcentration that is between 1× and 100× that of the platinum source.Again, too low concentrations of the Oxalic Acid can result in a lowplatinum film quality or incomplete platinum plating (e.g., anon-continuous platinum film). Higher concentrations of Oxalic Acid canresult in wasted chemicals. The concentration of Oxalic Acid can beselected to control deposition rate of the platinum, platinum filmquality, and grain size of the platinum film.

High quality immersion platinum platings can often be characterized by ahigh platinum particle density and a small grain size that produces acontinuous thin film platinum plating on the metal substrate. Incontrast, low quality platings can often be characterized by a platingthat is not continuous due to large grain size and/or low particledensity. Visual inspection of the plated article (e.g., using theunaided eye or magnifying devices such as a magnifying glass, amicroscope, a SEM, a TEM, etc.) can be used to determine the quality ofthe plating. A high quality plating will appear bright and shiny to theeye and will have a small grain size when viewed using a magnifyingdevice such as a microscope, SEM, or the like. On the other hand, a lowquality plating will not have the luster (i.e., bright, shiny,reflective) of a high quality film and visual inspection will typicallyreveal large grain size and low platinum particle density.

In that the complexing agent is an acid, the overall immersion platinumplating solution in this example is also acidic. A buffer agent can beused to maintain the overall pH of the solution, preferably at a pHbetween 1 and 6, and more preferably between 2 and 5. Examples of bufferagents include but are not limited to Ammonium Chloride (NH₄Cl), CitricAcid, and Acetic Acid. The temperature of the immersion platinum platingsolution preferably is maintained in a range from about 10° C. to about50° C. during contact with the metal substrate being plated. Forexample, the immersion platinum plating solution can be at roomtemperature (e.g., approximately 20° C. to 25° C.). The pH andtemperature can be selected to control plating rate, grain size, andquality of the platinum film.

The metal substrate can be various types of metal. Examples of metalsinclude but are not limited to copper Cu, tin Sn, nickel Ni, rutheniumRu, titanium Ti, aluminum Al, tantalum Ta, palladium Pd, rhodium Rh,iridium Ir, silver Ag, gold Au, cobalt Co, and alloys of those metals.The substrate may also be a metal alloy, rather than a pure metal.

The immersion platinum plating solution may also include additionaladditives including but not limited to the following: an inhibitorand/or accelerator to control the rate of the plating reaction; asurfactant; and an anti-oxidant, for example. Examples of inhibitorsinclude but are not limited to Benzotriazole (BTA). BTA and Thiourea aremore commonly used for corrosion resistance. Examples of acceleratorsinclude but are not limited to Hydroxylamine (NH₂OH—HCl) and SulfonicAcid. Examples of surfactants include but are not limited to TritonX-100, Cetyltrimethylammonium Bromide (CTAB), and Polyethylene Glycol(PEG). Examples of anti-oxidant include but are not limited toRiboflavin (Vitamin B2), Ascorbic Acid (Vitamin C), Oxalic Acid itself,and Hydroylamine.

Continuing the above example, an immersion platinum plating solutionuses BTA as an inhibitor with a concentration of between about 10 mg/Land about 100 mg/L, hydroxylamine as an accelerator with a molarconcentration that is between 1× and 20× the molar concentration of theplatinum source, Triton X-100 as a surfactant with a concentration ofbetween about 10 ppm and about 100 ppm, and an anti-oxidant with a molarconcentration that is between 1× and 20× the molar concentration of theplatinum source.

Note that the various additives described above do not have to beseparate components. It is possible for a single component to play therole of more than one additive. For example, Oxalic Acid can function asboth a complexing agent and as an accelerator. As another example,Oxalic Acid can function as both a complexing agent and as ananti-oxidant operative to prevent the Pt (II) from oxidizing into Pt(IV).

One advantage of this immersion plating is that it works, as will bedescribed in greater detail below. The inventors do not know of anysuccessful efforts to immersion plate platinum in a continuous thinfilm. Another advantage is that the plating can be controlled to providerelatively thin platinum plating, for example final thicknesses of 300Angstroms, 200 Angstroms, or 50 Angstroms or less, but still as acontinuous film. Thinner platinum plating consumes less platinum, thussaving on platinum costs and cost of the plated article.

In one approach, the final thickness is controlled by contact timebetween the article being plated and the immersion platinum platingsolution. The immersion platinum plating solution contacts the metalsubstrate (e.g., the workpiece to be plated) and, when the desiredthickness is achieved, the contact is broken to prevent further plating.In a different approach, the final thickness is controlled by thechemistry of the plating solution.

Contact between the immersion platinum plating solution and the metalsurface/substrate can be achieved in many different ways. In oneapproach, the plating solution is contained in a bath, and the metalsubstrate is dipped (e.g., submerged) into the bath. A structure (e.g.,a tank) containing a bath of the immersion platinum plating solutionpreferably is not reactive (e.g., made from a non-metal material) andthe bath preferably is temperature controlled. Examples of suitablematerials include but are not limited to plastic, Teflon®, PVDF, PEFA,quartz glass, Pyrex®, and other types of glass. The solution andsubstrate may also be agitated relative to each other, for example byagitating the solution (e.g., mechanically or by ultrasound) or bymoving the substrate. In a variation, the metal substrate may be movedthrough the bath, for example on a conveyor belt (which itself may ormay not move through the bath).

In some applications, it may be desirable to prevent relative movementbetween the article being plated and the solution. For small batches(e.g., plating a ring), the plating can be performed in a glass beakeror flask, for example. As another example, if a flask is used, a stopperor the like can be used to seal the mouth of the flask during plating.The flask or beaker can be placed on a temperature controlled hot plateor other heat source to set the temperature of the immersion platinumplating solution. A magnetic stirrer can be used to circulate theimmersion platinum plating solution over the article being plated. Acombination hot plate and magnetic stirrer can be used to provide bothtemperature control and relative motion between the article being platedand the immersion platinum plating solution. Preferably, the magneticstir bar used with the magnetic stirrer is encased in a non-metallicmaterial (e.g., a plastic encapsulated magnet) so that the solution willnot plate onto the stir bar.

In another approach, the immersion platinum plating solution can besprayed (e.g., as a mist, a vapor, or a stream) onto the metal surfaceto make the contact between the immersion platinum plating solution andthe metal surface/substrate. The solution is then washed off (e.g.,contact is broken) at the appropriate time. In some applications, it maybe desirable to have the metal surface facing upwards. For example, incertain types of semiconductor processing, it may be desirable todeposit (i.e., plate) platinum onto certain areas (e.g., microelectronicstructures) of a partially or fully processed semiconductor wafer, andit may be desirable to do this with the wafer facing upwards rather thandownwards or sideways. In one approach, the wafer is positioned facingupwards and the immersion platinum plating solution is then depositedonto the upwards-facing wafer. The solution can be distributed acrossthe wafer by spinning the wafer. The solution can be removed by washingit off, or by spinning the wafer at a high speed. For example, water(e.g., purified water or DI water) can be used to rinse the solution offof the plated article. In other applications, the wafer can be submergedin the immersion platinum plating solution in an upward facing position.In other applications, the immersion platinum plating solution can besprayed onto the wafer.

In yet other applications, the wafer can be facing downward, sideways,or in some degree of vertical orientation and then submerged in theimmersion platinum plating solution or the solution can be applied byspraying or some other form of application. Structures on the wafer thatare not to be immersion plated can be protected or covered by anon-metallic material such as an oxide or nitride, for example.Structures to be immersion plated can be part of an electrical circuit,an electrical contact, a mechanical component (e.g., a MEMS structure),or a nano-size structure, for example.

Another advantage of immersion plating is that it is generallynon-directional. Thus, irregularly shaped substrates can be successfullyplated because the immersion platinum plating solution typically has nopreferred direction for its plating action relative to the article beingplated. Jewelry and catalytic converters are two examples. The immersionplatinum plating solution can penetrate small orifices, crevices,features, and the like in a structure such as the micro ducts in acatalytic converter substrate. The immersion platinum plating solutioncan be used to immersion plate platinum on a metal surface to form acatalytic surface for a catalytic reaction between the platinum andanother chemical compound (e.g., as in the micro ducts of a catalyticconverter used with combustion engines). Fine features, intricatedetails, and complex surface shapes in jewelry can be plated with acontinuous thin film of platinum using the immersion platinum platingsolution.

Immersion platinum plating is further explained by the followingexamples. These are examples and are not intended to limit the scope ofthe invention.

Example 1

The following immersion platinum plating solution was created: 5 mMNa₂PtCl₄ as the platinum source, 5-200 mM (preferably 15-160 mM, andmore preferably 100-120 mM) Oxalic Acid as a complexing agent, and 0-50mg/L BTA as an inhibitor. As was described above, the Oxalic Acid canserve multiple functions in the immersion platinum plating solution. Inthis example, the Oxalic Acid also serves as an accelerator. Thesolution was maintained at a pH in a range of 1.8 to 2.5 (preferably 2.0to 2.2) and at a temperature of approximately 40° C. A tin (Sn)substrate was immersed in the solution for 60 sec. The resultingplatinum plating was bright and shiny.

The bright and shiny appearance of the platinum plated substrate is onemeasure that the platinum plating of the tin substrate was a continuousthin film. The plated tin substrate also passed a simple nitric acid(HNO₃) test designed to determine if the thin platinum film wascontinuous and therefore operative to protect the underlying tinsubstrate from being chemically attacked by the nitric acid. If theplated platinum film were not continuous, then the nitric acid wouldhave attacked those portions of the tin substrate that were not platedwith the corrosion resistant platinum. The nitric acid test did notreveal any signs of corrosion of the underlying tin substrate.Consequently, there were no discontinuities in the platinum plating andthe absence of discontinuities is indicative of a continuous thin filmlayer of immersion plated platinum on a tin substrate. The thickness ofthe plated platinum film was about 30 Angstroms as measured by atransmission electron microscope (TEM).

Example 2

The bath described in Example 1 above was used again for plating oneweek later. The performance of the plating solution was the same aftertwo plating iterations. Subsequently, the same bath was used for threeconsecutive weeks and the results were the same after a total of fiveplating iterations using the same bath. That is, the bath was notreplenished or refreshed with new chemicals or solutions. Therepeatability of the results indicated that the bath is chemicallystable over time.

Example 3

The following immersion platinum plating solution was created: 5 mMH₂PtCl₆ as the platinum source, 10 mM Oxalic Acid as a complexing agent,and 50 mg/L BTA as an inhibitor, and a pH in a range from about 2.5 toabout 3. A substrate of electrolessly deposited nickel (Ni) was immersedin the immersion platinum plating solution for about 10 minutes at roomtemperature. The resulting platinum plating was bright and shiny, andindicative of a continuous thin film platinum plating on the Nisubstrate.

One advantage of the immersion platinum plating solution is that it canbe used for plating items in small batches of one or more items and itcan be used for plating items in large production quantities. A singleitem or a batch of items can be plated using the solution. As a firstexample, a small jewelry shop can use the immersion platinum platingsolution to plate a metal surface of a single article of jewelry or afew articles of jewelry at the same time. The immersion platinum platingsolution can then be stored and subsequently used to plate otherarticles of jewelry at a future time. As a second example, the immersionplatinum plating solution can be used in a manufacturing or productionenvironment where large quantities of items are immersion plated at thesame time (e.g., a core element of a catalytic converter, contacts in anelectrical component, a medical device or component of a medical device,etc.).

Actual plating apparatus will be application specific and will depend onmany factors, such as the quantity of items to be immersion plated,plating time, plating temperature, processing environment, compositionof the immersion platinum plating solution, recycling and/orreplenishing one or more components of the immersion platinum platingsolution if necessary, removal of contamination from the immersionplatinum plating solution that may be caused by the process and/or theitem(s) being plated, agitation of the solution or relative movementbetween the solution and the article(s) being plated, just to name afew.

In FIG. 2, a configuration 200 depicts one example of how an article(s)can be plated with a thin continuous film of platinum using theimmersion platinum plating solution described above. Here, anon-metallic structure 201 (e.g., a tank or other type of container orvessel) is filled with the immersion platinum plating solution 210 to adepth sufficient to cover the articles to be plated. The structure 210can be a sealed container (not shown) or can have an opening 203 asdepicted. The solution 210 and articles to be plated can be positionedin the structure 201 via the opening 203. A sealed container may bedesirable to prevent contamination of the solution 210 and/or thearticle(s) to be plated or to the protect workers or the environmentfrom the solution 210. A portion or all of an article to be immersionplated can be positioned in the solution 210. For example, the entirearticle can be positioned below a surface 210 s of the solution 210 oronly a portion of the article to be immersion plated can be positionedbelow the surface 210 s (e.g., the portion having the metal surface(s)to be immersion plated) with a remaining portion positioned above thesurface 210 s.

Workpiece holders 202 can be used to insert 204 i and remove 206 r aworkpiece 211 into (e.g., make contact) and out (e.g., break contact) ofthe solution 210. Although the workpiece 211 can be any object for whichat least a portion comprises a metal surface to be plated, in theexample of FIG. 2, the workpiece 211 comprises a ceramic block for acatalytic converter and includes a lattice work or honeycomb structureof micro ducts 212 that are to be plated using the immersion platinumplating solution 210 to plate Pt onto the surfaces of the micro ducts212 to form a substrate of platinum (Pt) and rhodium (Rh) or platinum(Pt) and palladium (Pd). In some applications, the Pt can be plated ontopellets for a catalytic converter instead of the micro ducts of aceramic substrate.

Heat 213 can be applied to the solution 210 to maintain the solution 210at a desired temperature during the immersion plating process. A closedloop monitoring system can be used to set the temperature of thesolution to a desired set point (e.g., a temperature sensor coupled witha process controller). Movement 215 (e.g., motion, vibration, shaking,agitation, etc.) can be imparted to the structure 201, the solution 210,the workpiece 211, or any combination of the foregoing. In someapplications, both heat 213 and movement 215 can be applied. Thesolution 210 can be added 220 and/or removed 230 during the immersionplating process to accomplish any number of process objectives,including but not limited to filling the structure 201 with the solution210, circulating the solution 210 during the plating process, filteringcontaminants from the solution 210, recycling the solution 210, coolingor heating the solution 210, imparting movement 215 to the solution 210,re-conditioning the solution 210, adding the aforementioned additives tothe solution 210, just to name a few.

The configuration 200 can be adapted to a production environment wherelarge numbers of articles are to be plated using the solution 210.Although only two articles 211 are depicted, the configuration 200 canbe expanded by enlarging the volume of the structure 201, the workpieceholders 202 can be increased or replaced by some other apparatus forbringing the articles 211 into contact with the solution 210, such as aconveyor apparatus or the like, preferably made from a non-metallicmaterial, for example.

The articles 211 to be plated will be specific to each application andthe present invention is not limited to the articles 211 depicted inFIG. 2. For example, the articles to be plated can comprise any metalstructure or substrate upon which it is desired to immersion plate acontinuous thin film layer of platinum. A timer, process controller, orother apparatus can be used to control the duration of time the articles211 and the solution 210 are in contact with one another. For example,after a predetermined immersion plating time has elapsed, an apparatus(not shown) connected with workpiece holders 202 can remove the articles211 from the solution 210. Subsequently, the apparatus can move thearticles 211 to a rinse station for rinsing the solution 210 off thearticles 211.

In FIG. 3, a configuration 300 depicts one example of immersion platingthat can be used for small production quantities. Here flask 301 isfilled to the desired level with the immersion platinum plating solution310 via a neck 306 or a nipple 308 of the flask 301. A stopper 304 canbe used to seal the neck 306 and can include an opening 304 s throughwhich a workpiece holder 302 can be inserted and optionally moved in adirection depicted by dashed arrow 309 m. Although not depicted, nipple308 can also be sealed with a stopper. Workpiece holder 302 includes twostructures 303 adapted to support the workpieces 325 and 327 during theimmersion plating process. Workpieces 325 and 327 comprise two weddingbands of different sizes that are to be plated with a continuous thinfilm layer of platinum. Workpieces 325 and 327 are positioned below asurface 310 s of the solution 310 under predetermined conditions (e.g.,solution 310 composition, immersion time, temperature, vibration ormotion) to immersion plate a thin film continuous layer of platinum onexposed metal surfaces of the workpieces 325 and 327. Other articles ofjewelry including but not limited to ear rings, necklaces, rings,components of a timepiece, etc., can be immersion plated in smallquantities using the configuration 300.

For large production quantities, the configuration 200 of FIG. 2 can beused to immersion plate a larger quantity of articles. Optionally, theflask 301 can be positioned on an apparatus 350 configured to apply heat313 and/or movement 315 to the immersion platinum plating solution 310.Apparatus 350 can be a combination magnetic stirrer and hot plate withone control 353 for setting a desired temperature for the solution 310and another control 355 for setting an agitation speed for a magneticstir bar 357. Preferably, stir bar 357 is a magnet encapsulated in anon-metallic material such as a plastic, ceramic, glass, Teflon, orPVDF, for example. Alternatively, the workpiece holder 302 can be moved309 m (e.g., moved up and down) by a machine connected with the holder302 or manually by hand, for example. A thermocouple or other type oftemperature sensor can be inserted 320 through the nipple 308 or thestopper 304 to monitor the temperature of the solution 310. The solution310 can also be circulated, filled, or removed via the nipple 308 usingtubing or the like connected with a pump, for example. A solution forrinsing off the immersion platinum plating solution 310 can also bedispensed into the flask 301 via the nipple 308 or the neck 306.Configuration 300 can be used in jewelry shop, a laboratory, a machineshop, or other environment where immersion plating platinum on a largeor small number of articles is desirable.

Although FIGS. 2 and 3 depict articles submerged in the immersionplatinum plating solution (210, 310), the present invention is notlimited to submerged articles. Any process, machinery, technique, or thelike operative to place or position the solution and the article intocontact with each other and then breaking the contact between thesolution and article can be used. The immersion platinum platingsolution can be applied to the structure to be plated in a variety ofways including but not limited to spraying the solution on thearticle(s), applying the solution to the article(s) as a vapor or mist,repeatedly dipping the article(s) in the solution, flowing the solutionover the article(s), applying the solution as the article(s) are spun(e.g., as in spin deposition application on a semiconductor wafer),connecting the article(s) to be immersion plated with a moving structuresuch as a conveyor belt or the like and passing the moving structurethrough a tank or bath that contains the solution, just to name a few.

Further, in FIGS. 2 and 3, the process (299 and 399) of immersionplating platinum (Pt) onto the metal surfaces of the workpieces (212,325, 327) does not require electricity, does not require electrodes asin conventional electroplating, and does not require a reducing agent asin conventional electroless plating.

Although several embodiments of an apparatus and a method of the presentinvention have been disclosed and illustrated herein, the invention isnot limited to the specific forms or arrangements of parts so describedand illustrated. The invention is only limited by the claims.

1. An immersion plating platinum solution free of a reducing agent,comprising: a platinum source having a molar concentration of between 1mM and 50 mM; and a complexing agent including Oxalic Acid having amolar concentration that is between 1× and 100× the molar concentrationof the platinum source; an inhibitor; and an accelerator.
 2. Theimmersion platinum plating solution of claim 1, wherein the inhibitorcomprises benzotriazole (BTA).
 3. The immersion platinum platingsolution of claim 2, wherein the BTA has a concentration of between 10mg/L and 100 mg/L.
 4. The immersion platinum plating solution of claim1, wherein the accelerator comprises hydroxylamine (NH₂OH—HCl).
 5. Theimmersion platinum plating solution of claim 1, wherein the acceleratorhas a molar concentration that is between 1× and 20× a molarconcentration of the platinum source.
 6. The immersion platinum platingsolution of claim 1 and further comprising: a buffer agent; asurfactant; and an anti-oxidant.
 7. The immersion platinum platingsolution of claim 6, wherein the buffer agent comprises ammoniumchloride (NH₄Cl).
 8. The immersion platinum plating solution of claim 6,wherein the anti-oxidant comprises riboflavin (vitamin B2).
 9. Theimmersion platinum plating solution of claim 6, wherein the anti-oxidantcomprises ascorbic acid.
 10. The immersion platinum plating solution ofclaim 6, wherein the anti-oxidant has a molar concentration that isbetween 1× and 20× a molar concentration of the platinum source.
 11. Animmersion plating platinum solution free of a reducing agent,comprising: a platinum source; a complexing agent including Oxalic Acid;a buffer agent; a surfactant; an anti-oxidant; an inhibitor; and anaccelerator; wherein the surfactant comprises a nonionic surfactant. 12.The immersion platinum plating solution of claim 11, wherein thenonionic surfactant has a concentration of between 10 ppm and 100 ppm.13. An immersion plating platinum solution free of a reducing agent,comprising: a Pt (II) platinum source having a molar concentration ofbetween 1 mM and 50 mM; Oxalic Acid as a complexing agent having a molarconcentration that is between 1× and 100× the molar concentration of thePt (II) platinum source; an inhibitor; and an accelerator having a molarconcentration that is between 1× and 20× the molar concentration of thePt (II) platinum source.